Large Hole Single Stick Or Small Hole Twin Stick D18

I am in the process of installing an SM420 behind a 225 dauntless. I have already rebuilt the tranny. There is currently a large hole D18 transfer case with single stick in it which I know is good. I purchased a small hole D18 with a twin stick, condition unknown. Should I put the twin stick (which I want) on the large hole or keep it on the small hole and use that. What are the advantages or disadvantages of all options I have. The small hole TC will be taken apart and checked before proceeding if that is the option. I need to know before I can order the adapter to mate the tranny to the TC.
Thanks in advance for all and any advice, it will be greatly appreciated.

 

You will have to cut/modify trans cover for the swap. Single stick vs twin come through the floor in different places. So you might as well make it the way you want to begin with. Rebuild kits are cheap and easy on the 18. Good opportunity to put some different gears in the t/c

 

I am already prepared for the floor cutouts as I have a new replacement transmission tunnel which I have not installed due to knowing I will be doing the transmission upgrade.

 

The large index case is actually stronger. Put your twin stick bearing retainer on it as you indicated.

 

If for no other reason, the ability to pull the t-case off without removing the bull gear first is worth the price of admission.

 

I put the twin sticks from an old small hole on the original large hole tcase. Best of both worlds. You’re really gonna like the sm420.

 

ya, i'd put the twin stick retainer on the large hole case.

 

Twin sticks on your big hole case, all day long! Cheers!

 

Thanks for all the replies. The twin stick on the big hole is what I was leaning to because I know the big hole does not need to be rebuilt. I will check everything out before hand and replace all seals and gaskets.
I was curious if there was a reason to keep the small hole, but now I am assured not.

 

just a note . you'll have to disassemble both transfer cases
to do the twin stick conversion

 

Keep it so that you have it like all of us, sitting under a table in your garage for 20 years after you build the large hole twin stick.

 

Are all the internal parts the same for a twin stick small hole and single stick large hole, assuming both are 1-1/4" intermediate shaft?

 

They are not all the same. You must match gears. Here is a chart The Novak Guide to Dana 18 & 20 Gears Interchange 1941-1979

 

Who would do something like that? I have 3...

 

so the reason i can't find parts isn't a lack of parts, just a lack of willingness to give up spares.

 

"Spares" is a relative term. I have no spare anything until I have 3 in stock for my own use.